This invention relates to paper handling devices and more specifically to paper transporters for use in conjunction with optical character readers.
It is well known in the art to scan a printed page with an optical character reader (OCR) or the like by mechanically transporting the page under a scanning pick-up head. One arrangement utilizes a high speed shuttle mechanism which reciprocates the page in a tray. Another arrangement, having well-known speed, handling, and cost advantages, is to carry the page on a rotating drum. As the page rotates under a scanner, the OCR reads a narrow section or swath of the page which usually corresponds to a single printed line. On successive revolutions, the scanner indexes to read an adjacent swath until the entire page is read.
One method of driving the transporter drum and securing the paper to the drum in the desired location and spatial orientation is to utilize two belts or sets of belts that substantially encircle the drum at both of its ends. The belts rotate the drum and simultaneously grip and transport the paper carried on the exterior surface of the drum. It has been found, however, that this arrangement has various disadvantages which severely limit its effectiveness in reading lines of print, and particularly multiple lines of print that extend over substantially the entire surface of a page. First, it is difficult to align the paper accurately so that each line of print lies in a plane that is substantially normal to the longitudinal axis of the drum. Second, if a proper alignment is achieved, it is often difficult to maintain this alignment throughout the relatively large number of revolutions required to read a standard type or printed page. For example, if the paper is initially inserted into the carrier at a slight angle, this misalignment will cause the page to advance longitudinally with each revolution. This in turn can cause the scanner to lose synchronization within a line or between lines, read portions of two or more lines in one scan, or completely omit certain lines. Further, even if the paper is inserted correctly, slight differences in the speed, orientation, or tension of the belts located at opposite ends of the drum can cause an objectionable skewing of the paper resulting in the progressive longitudinal shift in the paper's position on the drum.
An alternative arrangement which avoids some of these problems utilizes a single belt mounted over a central portion of the rotatable drum and substantially encircling the drum except for a relatively small entrance and exit clearance formed between the looped belt ends. This arrangement, however, is unsuitable for reading pages of printed documents since the belt obscures a portion of the print. Another problem is that after a period of operation, the belt tends to accumulate the ink or pencil material forming the printed characters and transfer it to subsequent pages being transported and read.
It is therefore a principal object of this invention to provide a paper transporter that automatically adjusts the page to an accurately predetermined location and orientation and transports the paper under the scanning pick-up head at a highly uniform speed.
Another object of this invention is to provide a paper transporter that has a rugged and uncomplicated design and operates with a high degree of reliability.
Still another object is to provide a paper transporter that does not transfer print material between successive sheets of paper being transported and scanned.
Yet another object is to provide a paper transporter having these advantages which obscures only a small edge portion of the page being transported and scanned.